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PublicationNumerical Modeling of the Redistribution of Residual Stresses in Deep Rolled Cross Bores in Shafts from GJS700-2( 2024)
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PublicationFine blanking of pre-hardened high manganese steel to investigate the sheared surface hardening and part quality( 2023)Fine blanking is a highly productive process for manufacturing of high accuracy sheet metal parts with functional surfaces. The specific process characteristic leads to high forming in the shear zone and an associated strain hardening of the sheared functional surfaces. Utilization of the process-immanent sheared surface hardening can reduce time and resources of downstream heat treatment processes such as case hardening. High Manganese Steels (HMnS) are characterized by a high strain hardening capacity due to the deformation mechanisms of twinning and transformation induced plasticity occurring during forming. As a result of high tensile strengths, HMnS are suitable as lightweight materials, but often exhibit a relatively low yield strength in terms of structural design features. One approach for increasing the strength values without changing the alloy design is a forming-induced strain hardening of the semi-finished sheet metal by means of upsetting. Therefore, this paper deals with an experimental investigation of the influence of pre-hardening on the blanked part properties during fine blanking of HMnS X40MnCrAlV19-2 LY (1.7401). For this purpose, sheet blanks were strain hardened by means of flat coining and subsequently fine blanked with an analog geometry representing tribologically stressed functional surfaces. Relevant functional surfaces were then analyzed by means of microhardness measurements with regard to the sheared surface hardening as well as characterized in terms of the quality-determining attributes die roll and clean-shear area. Due to the deformation mechanism of twinning, fine blanking of pre-hardened HMnS resulted in a combination of process-immanent high sheared surface hardening and increased yield strength with simultaneous optimal functional surface quality.
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PublicationModification of the surface integrity of powder metallurgically produced S390 via deep rolling( 2023)Fine blanking is an economical process for manufacturing sheet metal workpieces with high sheared surface quality. When machining high-strength steels, material fatigue leads to increased punch wear, which reduces the economic efficiency of the process. This fatigue of the cutting edge and lateral punch surface can be counteracted by mechanical surface treatments. Deep rolling has proved particularly useful for such surface modification, as it allows both: machining of the lateral punch surface and the application of the cutting edge rounding required for fine blanking. For the precise design of the fine blanking punch contour especially the macroscopic deformation of the workpiece is decisive. In this paper, the possibility of specifically modifying the surface integrity of hardened and powder metallurgically produced S390 by means of the incremental surface treatment process deep rolling is investigated. By varying the decisive process parameters rolling pressure, ball diameter and step over distance, their influence on surface integrity is determined. The surface integrity is afterwards characterized by macro hardness, surface topography and residual stress state and microstructural images.
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PublicationA Model Calculation of CO2 Emissions Saving Potential for Fine Blanking of Inductively Heated Sheet Metal with Comparison of the Product Variants( 2023)The steel processing industry must increasingly question itself with regard to environmental aspects, especially for automobile production. As a consequence of the resulting lightweight construction requirements in the automotive sector, manufacturing processes of industrial relevance must deal with high-strength steels. In case of fine blanking, the process faces its limits already when processing medium-high tensile strength steels because of high tool wear or failure. A promising approach to overcome these process limits is the introduction of heat into the processed metal sheet in order to lower the flow stress of the steel. In order to estimate the sustainability of a fine blanking process with inductively heated sheets, the energy input during heating is investigated in this work. An energy balance is drawn for fine blanking of inductively heated sheets. A further component of the work is the subsequent use phase of the components produced in this way. A consideration of the greenhouse gas emissions savings potential by fine blanking in the German automotive production shows possible future perspectives for manufacturing. It could be found that by substituting standard fine blanking process by inductively heated fine blanking of higher strength steels greenhouse gas emissions can be decreased.
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PublicationCoefficient of friction of cemented carbides machined by sinking EDM( 2023)Cemented carbides possess properties that predestine them as a durable tool. However, these properties hinder conventional machining, which is why Electrical Discharge Machining (EDM) is a promising alternative. Three different EDMed cemented carbides were compared with a ground surface in a pin-on-disk test setup. They were evaluated under dry and lubricated conditions with two distinct antibody materials. The tests did not reveal a correlation between the surface roughness of the cemented carbide pins and the coefficient of friction. However, some test sets yielded very different results, which is why particular considerations should be made with new sliding compositions.
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PublicationChevron cracking during full forward impact extrusion of aluminum alloy EN AW 7075 in dependence of heat treatment condition and tribological system( 2023)In addition to the growing demand for energy efficiency, the current and future legal emission limits in the transport sector lead to an increasing demand for weight-reduced components. By substituting conventional materials with weight-reduced components, such as the aluminum alloy EN AW 7075 (AlZn5.5MgCu), emissions during vehicle service life can be reduced. Chevron cracks, also called internal cracks, can be caused by a variety of reasons during cold extrusion processes and pose a great, non-visible challenge for product quality [1]. However, the cause effect relations between the heat treatment condition and the tribological system in regard to damage development have not yet been sufficiently analyzed. In order to examine these relations, the first forming step of a ball pivot was investigated using full forward impact extrusion. Experiments with different tribological systems were investigated by varying lubricant and die treatment with regard to friction and wear reduction. In addition, the effect of the workpiece formability on crack formation was examined by comparing the T6 and soft annealed state of EN AW 7075 as workpiece materials. During this study, the microstructure of both conditions was investigated to highlight differences. A validated FE process simulation using the simulation software Forge NxT 3.2 accompanied the process in order to evaluate the stress state during the full forward impact extrusion process and its relation to the occurrence of chevron crack formation. In the experiments conducted during this study, chevron cracking occurred during full forward impact extrusion of EN AW 7075 in state T6, while in soft annealed condition none appeared. Unlike the heat treatment condition, the tribological system had no impact on the occurrence of chevron cracking but on the severity of the cracks.
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PublicationInfluence of process parameters and process set-up on damage evolution during stretch drawing of u-shaped profiles( 2023)The damage state in the form of voids and lattice defects of a sheet metal component has a substantial impact on the performance of a component in service regarding fatigue or crash behaviour. Therefore, managing the damage evolution during forming, especially the accumulation and distribution of damage, by targeted changes of the process parameters and set-up enables to improve component performance by influencing the stress-strain state [1]. The evolution of the stress-strain state during the forming process and along the process route represents the most significant factor influencing the resulting damage state. This paper focuses on the influence of the damage state of sheet metal components in order to improve the performance of a component regarding fatigue and crash behavior. Considering a variation of the process parameter (drawing die radius) and change in process set-up (singlestep, multistep, reverse stretch drawing) the damage accumulation and distribution within the component is analyzed using a calibrated LEMAITRE damage model. For the consideration of this paper, an u-shaped geometry of dual phase steel DP800, which is often found as an element in vehicle body construction, is used.
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PublicationFine Blanking Limits of Manganese-Boron-Steel in Fine Blanking Compared to Tempered Steel with Variation of Sheet Metal Temperature( 2022)Fine blanking is a key technology for the near-net-shape production of sheet metal components. It is often used in combination with processes such as deep drawing. With increasing environmental requirements, the processing of materials with lightweight construction potential is becoming more and more important. A group of materials with high potential for lightweight construction, not only due to their suitability for hot stamping, is the group of manganese-boron steels. The fine blanking properties of these steels have not yet been exhaustively investigated. In this work, the fine blanking properties of the manganese-boron steel 40MnB4 were investigated in comparison to the quenched and tempered steel 42CrMo4. This was done using a star-piece fine blanking layout with investigation of die roll as well as tooth tip cracking. Furthermore, an investigation of the hightemperature fine blanking properties were investigated by means of inductive heating prior to fine blanking. The process forces were evaluated depending on the sheet metal temperature. A good fine blanking capability of 40MnB4 could be confirmed. Process forces and product quality were comparable to 42CrMo4 steel. Accordingly, an industrial application of fine blanking to manganeseboron steels seems highly promising.
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PublicationSystematic Change of Abrasive Size Distribution( 2021)The continuous suspension (ConSus) technology is a new coming approach that promises performance advantages over industrially used abrasive waterjet (AWJ) systems in production scenarios. However, it currently lacks practical experience and process parametrization is typically still empirical of either using a 2-phase abrasive suspension jet (ASJ) or a 3-phase injection AWJ tool. A practical comparison of respective AWJ tool characteristics of prior work piece contact is needed for fundamental parametrization. An experimental approach was used to compare the respective AWJ systems. The abrasive material was compared before and after going through either an injection AWJ head or a ConSus ASJ system. Typical abrasive materials and mesh sizes for AWJ machining were systematically investigated. This paper shows that current AWJ cutting systems yield different results when using equal abrasive material. ConSus shows almost no significant effect on abrasive size distribution while commonly used injector systems shifts a tremendous portion of the original abrasive to smaller grain sizes. Therefore, the results enhance process understanding and revision of existing process models for future applications.
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PublicationElectrochemical defect analysis (EC-D) of additive manufactured components( 2021)Due to more freedom in design and flexibility in production, parts produced by additive manufacturing technologies (AM) offer a huge potential for the manufacture of turbomachinery components. Because of the layer by layer built structure, internal defects like cracks or gaseous pores can occur. These defects considerably reduce the mechanical properties and increase the importance of quality control, especially in the field of turbomachinery. Therefore, in this study, an electrochemical defect analysis (EC-D) of additive manufactured components is introduced, performed and validated in comparison to a nondestructive X-ray testing of the same part. A test rig was developed, which allows an alternation between electrochemical machining and subsequent optical documentation of each removed layer. The documentation of the surface and the macroscopic defects in the AM-parts are captured by an integrated camera system.
